Interpretive Summary: The purpose of this research was to determine whether tarbush leaves contained herbicidally active constituents. Tarbush leaves were extracted with various solvents, and each extract was tested on plants.The herbicidal activity of the most active fraction(ether) was investigated in more detail on several weed and crop species. Tarbush leaves contain natural products that are highly phytotoxic and may be useful for weed management.

Technical Abstract:
Growth of selected weed and crop species was inhibited by crude extracts of tarbush incorporated in soil at a 1 mg/g level. The phytotoxic effects were not lethal, but growth and development of seedlings was delayed. Inhibition of shoot development was evident at younger developmental stages with as much as 32, 34, and 37% reduction in size for blue panicum, soybean and yellow nutsedge, respectively, but most seedlings, except the grasses (blue panicum and canarygrass), appeared to recover within 14 d of growth. Root growth was inhibited more than shoots growth, and weeds were more sensitive than the crop species tested. Root biomass of ivyleaf morningglory and sicklepod was reduced by 80 and 74% relative to control, respectively. Soybean was more sensitive than corn, with 58 and 15% reduction in root dry weight, respectively. The phytotoxic activity of tarbush extract does not appear to be associated with inhibition of mitosis in spite of the dramatic inhibition of root development observed on certain species.